<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        input{
            position: relative;
            top: 80px;
            left:600px;
            background-color: #00BFFF;
            width: 90px;
            height:60px ;
            text-align: center;
            line-height: 60px;
        }

    </style>
</head>
<body>
    <input type="button" onclick="calArea(prompt('请输入圆的半径'))" value="计算圆的面积" align="center">
<script>
    function calArea(radius){
        let a=3.1415926;
        alert("半径是"+radius+"  "+"圆的面积是："+a*radius*radius);
    }


</script>



</body>
</html>


